[Wallet] Fix decimals keyboard in some Samsung devices (#5926)

### Description

On some Samsung devices, the numpad when inputting decimal amounts was not showing the decimal separator (dot or comma).

This is because these Samsung devices apparently have the same value for the decimal pad constant than for the autocapitalize constant, which causes them to override each other (🤦 ).

### Tested

On a Samsung device:

Before:
![Screenshot_2020-11-20-13-31-32](https://user-images.githubusercontent.com/6062888/99824926-217c7e00-2b35-11eb-859c-79fefd2c9346.png)

After:
![Screenshot_2020-11-20-13-31-23](https://user-images.githubusercontent.com/6062888/99824924-204b5100-2b35-11eb-932c-9958f46d53f7.png)


### Related issues

- Fixes #1309

### Backwards compatibility

N/A

packages/mobile/src/components/CeloAmountInput.tsx

@@ -51,6 +51,7 @@ export default function CeloAmountInput({
       placeholder={'0'}
       placeholderTextColor={colors.gray3}
       keyboardType={'decimal-pad'}
+      autoCapitalize="words"
       onChangeText={onCeloChanged}
       value={celo}
       testID={'CeloAmount'}

packages/mobile/src/exchange/ExchangeTradeScreen.tsx

@@ -309,6 +309,7 @@ export class ExchangeTradeScreen extends React.Component<Props, State> {
             <TextInput
               autoFocus={true}
               keyboardType={'decimal-pad'}
+              autoCapitalize="words"
               onChangeText={this.onChangeExchangeAmount}
               value={this.getInputValue()}
               placeholderTextColor={colors.gray3}

packages/mobile/src/exchange/__snapshots__/ExchangeTradeScreen.test.tsx.snap

@@ -82,6 +82,7 @@ exports[`ExchangeTradeScreen renders correctly 1`] = `
         </View>
         <TextInput
           allowFontScaling={true}
+          autoCapitalize="words"
           autoFocus={true}
           keyboardType="decimal-pad"
           onChangeText={[Function]}

packages/mobile/src/exchange/__snapshots__/WithdrawCeloScreen.test.tsx.snap

@@ -183,6 +183,7 @@ exports[`WithdrawCeloScreen renders correctly 1`] = `
       >
         <TextInput
           allowFontScaling={true}
+          autoCapitalize="words"
           keyboardType="decimal-pad"
           onChangeText={[Function]}
           placeholder="0"